The world is today asking: "How did two young ethnic Chechens come to
bring bloodshed to the streets of America?"

The answer lies in the way that conflict in Russia's North Caucasus has changed over time from a nationalist struggle to an Islamist insurgency, connected to the ideology of global jihad.

When Dzhokhar Tsarnaev, the Boston bomber who is still on the run, was born in 1993, his namesake, Dzhokhar Dudayev, was about to lead the Chechen rebels in one of the greatest battles on Russian soil since Stalingrad.

When the Soviet Union dissolved in 1991, Dudayev, a former Soviet air force general, declared Chechnya's independence, imagining that he would create a prosperous and secular republic.

But Dudayev was killed by a Russian missile in 1996. Chechen forces – incredibly – managed to achieve victory over the Russian war machine, despite its carpet-bombing of the capital, Grozny, in a two-year campaign, and secured de facto independence.

Peace did not last for long. Warlords and criminals flocked into the tiny unrecognised republic. And with them came Islamist radicals looking for a new theatre for holy war.

Chechnya increasingly became a magnet for extremists who wanted not just to defeat Russia, but strike the West in general and America in particular. By 1999, when the republic had become a black hole of kidnapping and violence, a new force was rising in Russia. Vladimir Putin oversaw a second brutal war to subdue Chechnya. He did so with total disregard for civilian life.

Mr Putin succeeded in ruthlessly reimposing the Kremlin's control over Chechnya, but with every passing year, the conflict became more religious and ideological. Chechen rebels struck Russian targets, capturing hundreds of hostages in a theatre in Moscow in 2002 and a school in the town of Beslan in 2004. They also developed a burning grievance against America and the West for supposedly aiding and abetting Russia.

In their minds, Russia and America were allies in a campaign against Islam.

The Obama administration might have fed that perception by blacklisting a Chechen warlord, Doku Umarov, as a "terrorist". He claimed responsibility for suicide bombings on the Moscow underground that killed 40 people in 2009.

On Friday, Ramzan Kadyrov, the Kremlin-appointed Chechen leader, denied any connection with the Tsarnaev brothers saying: "They grew up in the United States, their attitudes and beliefs were forged there. It is necessary to seek the roots of this evil in America."

But al-Qaeda's ideology appears to have found increasingly fertile ground among Chechens. It seems doubtful whether the Tsarnaev brothers ever visited their ancestral home, yet thousands of miles away in Boston they could have fallen under this spell.